1. Field of the Invention
This invention relates to a reversibly mountable baffle plate for supporting a bottom hole survey apparatus within a directional drilling string.
2. Description of the Prior Art
In directional drilling environments associated with the exploration and production of hydrocarbons it is often necessary to ascertain accurately the orientation of a bore being generated through formations of the earth's surface with respect to a predetermined datum. Simultaneously, it is desirable to provide information concerning the vertical declination of the bore hole from true vertical. Also, in some instances, it may be desirable to ascertain the direction of the drilling bit generating the bore. To accomplish these three aforementioned purposes the prior art inserts into the bore being generated a suitable survey apparatus such as that disclosed and claimed in the co-pending application Ser. No. 821,461, filed Aug. 3, 1977, now U.S. Pat. No. 4,141,153, and assigned to the assignee of the present invention. With the bottom hole survey apparatus disposed within the directional drilling string the orientation of the drilling string with respect to the predetermined datum, as well as the vertical declination and bit orientation, may be determined.
Typically, in operation, the bottom hole survey apparatus may be pumped down or lowered by a wire line through the interior of the directional drilling string until a mule shoe element usually provided on the lowermost axial end of the survey apparatus receives and engages a radially inwardly directed pin. The inwardly directed pin is secured to the directional drilling string in a predetermined relationship with the drill bit. With the receipt of the pin in the slot of the mule shoe, the instrumentation connected within the bottom hole survey apparatus is placed in a predetermined axial alignment with the drill bit such that an accurate determination of the direction of the bore generated by the bit may be obtained. Arrangements as that just described are typically utilized in connection with bottom hole survey apparatus wherein the instrumentation includes photographic equipment operable to provide a photographic print illustrating the orientation of a plum bob with respect to a transparent disc having an array of concentrically disposed lines scribed thereon to indicate the vertical declination of the bore hole.
Alternatively, in those cases where the vertical declination of the bore is desired but where the directional orientation of the bit is not required, it is common practice in the art to replace the mule shoe with a suitable landing sub and to dispose therein a member known in the art as a baffle landing plate. The baffle plate is disposed in the drill string prior to the insertion of the drill string into the bore hole to thereby form a false bridge or false bottom onto which the instrument package is landed. It is again noted that the baffle plate is disposed in place of the mule shoe sub, and inserted in a manner so as to present only a minimal impedence to the flow of well fluid. The baffle plate generally includes an outer ring secured by an array of webs to a concentrically disposed inner member. The inner member is spaced axially with respect to the outer ring and supported in position by the array of webs. In cross-section, the orientation of the inner ring (when supported by the webs) with respect to the outer ring defines a substantially frusto-conical arrangement. In operation, the narrow diameter of the frustum is disposed toward the surface. The webs define a plurality of openings which permit well fluid to flow through the directional drilling string while the lower end of the bottom hole survey apparatus is received within the opening defined in the inner ring. It has been observed that only if the baffle plate is disposed within the directional drilling string such that the inner ring is proximal to the surface will flow be permitted through the openings provided by the webs when the directional drilling element is associated with the baffle plate and supported thereby. If this described arrangement is reversed, the combination of the survey apparatus and the baffle plate act to undesirably throttle the flow. Accordingly, it is necessary to precisely and accurately insert the baffle plate into those sections of drill pipe disposed next-above the directional drilling elements prior to insertion of the directional drilling element into the well bore. As noted, the consequence of improper insertion of the baffle plate within the drill string is the potential inhabition or blockage of the flow of well drilling fluid during that period of time when the lowermost axial end of the survey apparatus is received in and supported by the baffle plate.
It would, accordingly, be advantageous to provide a baffle plate for receiving and supporting the lowermost axial end of a bottom hole survey apparatus within the interior of a directional drilling string such that the flow of drilling fluid is neither inhibited nor blocked when the bottom hole survey apparatus is received in and supported thereby. It would be a further advantage to provide a baffle plate for supporting the lower axial end of a bottom hole survey apparatus that may be interchangeably mounted between adjacent drill pipe sections without regard to the orientation of the baffle plate as the drill string is assembled.